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Consultant Engineering Services Detailed Assessment Report
Kingston Biosolids and Biogas Master Plan
PRESENTED TO
Utilities Kingston
JULY 2019 ISSUED FOR USE FILE: 704-SWM.SWOP03442-01
Tetra Tech Canada Inc. Suite 201 – 111 Farquhar Street Guelph,
ON N1H 3N4 CANADA
Tel 519.803.3042
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EXECUTIVE SUMMARY Tetra Tech Canada Inc. (Tetra Tech) was
originally tasked to investigate the potential of utilizing the
current assets of Utilities Kingston (UK) to produce Renewable
Natural Gas that could then be used to reduce the carbon footprint
of the City of Kingston. This report is a follow-up to the
“Preliminary Assessment Report,” which was used to outline options
that could be implemented, and was followed up with a selection of
the most viable set of options.
The work was initially triggered by UK’s interest to identify
alternative systems to: manage biosolids and enhance biogas
production, review the alternative sites best suited to undertake
the enhancements, and identify the best options (and investment
needed to implement the options).
At the outset of the study, the provincial government was
promoting two initiatives that impacted this study, namely Cap and
Trade and Zero Waste. With the change in government the Cap and
Trade regulation has been eliminated and government initiatives
regarding waste management are in the preliminary policy stage.
These changes impacted the study, the outcomes are outlined
below.
The Detailed Study has included the following steps:
1. A review of the current operations including technologies
used and throughput.
2. A review of six options plus the inclusion of dewatering.
These are:
− Do Nothing. – Status quo with upgraded digesters at Catarqui
Bay.
− Option 2A – Expansion of the existing Mesophilic Anaerobic
Digestion (MAD) process with capability tooperate in Temperature
Phased Anaerobic Digestion (TPAD) undertaken at Cataraqui Bay.
− Option 2B – Expansion of the existing MAD process with the
inclusion of Biological Hydrolysis (BH) upfront of MAD undertaken
at Cataraqui Bay.
− Digestion undertaken with BH at Ravensview.
− Inclusion of Source-Separated Organics (SSO) undertaken with
2B (above).
− The construction of a new Digestion Facility at Knox Farms (or
another City location).
The resultant review of options, both from a technical and
financial perspective were:
Option 2B, Biological Hydrolysis (BH) is recommended regardless
of its location (Cataraqui Bay, Ravensview,or another
location).
RNG injection to pipeline is recommended over increased
electrical production or Compressed Natural Gas(CNG) as the carbon
premium is significantly higher in value.
Cataraqui Bay is favoured over Ravensview since the summer
natural gas consumption downstream ofRavensview is significantly
lower than what will be generated.
Dewatering is recommended for any of the selected sites.
When comparing upgrading the Cataraqui Bay digesters, the
selection of an alternative site is considered equalin terms of
financial value.
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The addition of SSO is highly viable in combination with BH with
the current waste flow generated from the Cityof Kingston. Further
addition of waste organics increases the financial payback.
In-house trucking of sludge is recommended to decrease the
haulage cost.
It is highly recommended that UK pursue federal or provincial
grant programs as funding from these seniorlevels of government
would have significant impact on the financial viability of the
respective options.
In all cases, Tetra Tech recommends that UK start initial
talks/negotiations with potential purchasers of the RNG to
establish the best possible prices. As part of the Master Plan
process UK also needs to proceed with stakeholder engagement to
ensure that the public has input in the future direction of UK.
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TABLE OF CONTENTS
EXECUTIVE SUMMARY
........................................................................................................................
I
1.0
INTRODUCTION..........................................................................................................................
1 1.1 Project Background
...............................................................................................................................
1 1.2 Detailed Assessment Approach and
Methodology................................................................................
2
2.0 DESCRIPTION OF EXISTING CONDITIONS
..............................................................................
3 2.1 The Study
Area......................................................................................................................................
3
2.1.1 Cataraqui Bay Wastewater Treatment Plant
............................................................................
3 2.1.2 The Ravensview Waste Water Treatment
Plant.......................................................................
6 2.1.3 The Cana Wastewater Treatment Plant
...................................................................................
7
2.2 Existing Biosolids Management
Processes...........................................................................................
7 2.2.1 Biosolids Characteristics, Quantities and Projections
.............................................................. 7
2.2.2 Existing Biosolids Treatment Capacity
...................................................................................
14 2.2.3 Biosolids Storage Requirements
............................................................................................
15
2.3 Existing Biogas Management Processes
............................................................................................
16 2.3.1 Biogas Characteristics, Quantities and
Projections................................................................
16 2.3.2 Existing Biogas Treatment
Capacity.......................................................................................
17
2.4 Pre-Selected Treatment Technologies
................................................................................................
18 2.4.1
PSA.........................................................................................................................................
18 2.4.2 Membrane Separation
............................................................................................................
19 2.4.3 Water
Wash/Scrubbing...........................................................................................................
20 2.4.4 Amine Scrubbing
....................................................................................................................
21 2.4.5 Recommended Process
.........................................................................................................
21
2.5 End-Use
...............................................................................................................................................
21
3.0 ALTERNATIVE BIOSOLIDS AND BIOGAS MANAGEMENT
OPTIONS................................... 23 3.1 Option 1 – Do
Nothing
.........................................................................................................................
23
3.1.1 Description of
Alternative........................................................................................................
23 3.1.2 Impact on Existing Facilities
...................................................................................................
24 3.1.3 Cost Analysis
..........................................................................................................................
25
3.2 Option 2 – Optimize Infrastructure at Cataraqui
Bay...........................................................................
26 3.2.1 Description of
Alternative........................................................................................................
26 3.2.2 Impact on Existing Facilities
...................................................................................................
28 3.2.3 Cost Analysis
..........................................................................................................................
31
3.3 Option 3 – Optimize Infrastructure at Ravensview
..............................................................................
31 3.3.1 Description of
Alternative........................................................................................................
31 3.3.2 Impact on Existing Facilities
...................................................................................................
32 3.3.3 Cost Analysis
..........................................................................................................................
34
3.4 Option 4 – Incorporate SSO at Cataraqui Bay
....................................................................................
34 3.4.1 Description of
Alternative........................................................................................................
34 3.4.2 Impact on Existing Facilities
...................................................................................................
35 3.4.3 Cost Analysis
..........................................................................................................................
39
3.5 Option 5 – Integrate Processing of Biosolids and SSO at Knox
Farms .............................................. 39
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3.5.1 Description of
Alternative........................................................................................................
39 3.5.2 Impact on Existing Facilities
...................................................................................................
40 3.5.3 Cost Analysis
..........................................................................................................................
43
4.0 FINANCIAL ANALYSIS OF ALTERNATIVES
...........................................................................
44 4.1 Alternative Biogas Utilization
Options..................................................................................................
44 4.2 Analysis of Other Options
....................................................................................................................
45
5.0 CONCLUSIONS AND
RECOMMENDATIONS...........................................................................
45 5.1 The Next Steps
....................................................................................................................................
46
6.0
CLOSURE..................................................................................................................................
47
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LIST OF TABLES IN TEXT
Table 1-1:Further Investigated Technologies
.........................................................................................
2 Table 2-1: Existing and Upgraded Treatment Technology
.....................................................................
3 Table 2-2 Cataraqui Bay and Ravensview WWTP Biosolids
Characteristics.......................................... 8 Table
2-3 Cataraqui Bay and Ravensview WWTP Biosolids Metal Content as
Compared to NMA
Standards.............................................................................................................................
9 Table 2-4 Cataraqui Bay WWTP and Ravensview WWTP Biosolids
Pathogen Content as Compared to
NMA Standards
....................................................................................................................
9 Table 2-5 Historical Annual Effluent and Biosolids Quantities in
Cataraqui Bay WWTP (2015 – 2017) 10 Table 2-6 Historical Annual
Effluent and Biosolids Quantities in Ravensview WWTP (2015 – 2017)
... 10 Table 2-7 Projected Annual Biosolids Production in Cataraqui
Bay WWTP up to Year 2037 ............... 11 Table 2-8 Projected
Annual Biosolids Production in Ravensview WWTP up to Year
2037................... 13 Table 2-9 Total Annual Biosolids
Production in Year
2037...................................................................
14 Table 2-10 Biosolid Process Design Parameters in Cataraqui Bay
WWTP.......................................... 14 Table 2-11
Biosolid Process Design Parameters in Ravensview WWTP
............................................. 15 Table 2-12
Biosolids Storage Requirements in Year 2037
...................................................................
15 Table 2-13 On-site biosolids storage capacities at Cataraqui Bay
and Ravensivew............................. 16 Table 2-14,
Potential Range for Purchase Agreements
.......................................................................
22 Table 3-1 Estimated Biosolids Production and Biogas Generation
in the Year 2037............................ 24 Table 3-2 Estimated
Biosolid and Biogas Production for Options 2A and 2B
....................................... 29 Table 3-3 Transportation
and Footprint Requirements for Option 2A and
2B....................................... 30 Table 3-4 Impact on
Biosolid Production and Biogas Generation of Option 3
...................................... 32 Table 3-5 Transportation
and Footprint Requirements for Option 3
..................................................... 33 Table 3-6
Impact on Biosolid Production and Biogas
Generation.........................................................
36 Table 3-7 Transportation and Footprint Requirements for Option 4
..................................................... 38 Table 3-8:
Change in NPV
...................................................................................................................
39 Table 3-10: Impact on Biosolid Production and Biogas Generation
of Option 5 ................................... 41 Table 3-11:
Transportation and Footprint Requirements for Option
5................................................... 43 Table 3-12:
Comparing 2B with SSO with Knox Farms with SSO
Results............................................ 43 Table 3-13:
Comparison with the Stand Alone 2B Option with and without
SSO.................................. 44 Table 4-1: Different
Generation Rates
.................................................................................................
44 Table 4-2: Different Generation Rates (SSO with Option
2B)...............................................................
44 Table 4-3: NPV Results (Electricity
Produced).....................................................................................
44
LIST OF FIGURES IN TEXT
Figure 2-1: Upgraded Cataraqui Bay Treatment Flow
Diagram..............................................................
6 Figure 2-2: Ravensview Waste Water Treatment Flow Diagram
............................................................ 6
Figure 2-3 Projected Biosolids Production in Cataraqui Bay WWTP up
to Year 2037 .......................... 12 Figure 2-4 Projected
Biosolids Production in Ravensview WWTP to Year 2037
................................. 13 Figure 2-5: Ravensview
Digester Gas
Production................................................................................
16 Figure 2-6: Cataraqui Bay Digester Gas Production
............................................................................
17 Figure 2-7: Biogas Treatment Technologies
.......................................................................................
18
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Figure 2-8: Pressure Swing Adsorption
................................................................................................
19 Figure 2-9: Membrane Separation
.......................................................................................................
19 Figure 2-10: Water
Wash.....................................................................................................................
20 Figure 2-11: Amine Scrubbing
.............................................................................................................
21 Figure 3-1 Existing Solid Treatment Process at Cataraqui Bay
WWTP................................................ 23 Figure 3-2
Existing Solid Treatment Process at Ravensview WWTP
................................................... 23 Figure 3-3
Upgrades to TPAD at Cataraqui Bay WWTP
......................................................................
27 Figure 3-4 Upgrades with Addition of BHP at Cataraqui Bay WWTP
................................................... 28 Figure 3-5
Upgrades of TPAD Process with Addition of BH system at Ravensview
WWTP................. 32 Figure 3-6 Incorporate SSO in Cataraqui
Bay
WWTP..........................................................................
35 Figure 3-7 SSO Resource Recovery and Co-digestion Process at
Knox Farm .................................... 40 Figure 3-8 Flow
chart - Options for Biosolids Residual Management at Knox Farm
............................. 42
APPENDIX SECTIONS
TABLES
Table 1 Master Plan Equipment Costs
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Acronyms/Abbreviations Definition
BAF Biologically Aerated Filter
BH Biological Hydrolysis
BH-AD Biological Hydrolysis-Anaerobic Digestion
CAS Conventional Activated Sludge
Cataraqui Bay Cataraqui Bay Wastewater Treatment Plant
CFU Colony-Forming Units
CH4 Methane
City City Of Kingston
CM2 Regulated metal content of a NASM exceeds that of CM1 NASM
but does not exceed the
concentration set out in Table 2 for aqueous or non-aqueous CM2
material, whichever applies
CNG Compressed Natural Gas
CO2 Carbon Dioxide
COD Chemical Oxygen Demand
CP1 Pathogen-based category based on Origin, typically based on
NASM Categories 1 and 2
CP2 Pathogen based classification defined as NASM Category 3
which includes sewage biosolids
EA Environmental Assessment
H2S Hydrogen Sulfide
HRT Hydraulic Retention Time
L&Y Leaf And Yard Waste
MAD Mesophilic Anaerobic Digestion
MEA Municipal Engineers Association
MECP Ministry Of Environment, Conservation, and Parks
MOP 8 Maximum Operating Pressure
N and N2 Nitrogen
NASM Non-Agricultural Source Materials
NMA Ontario Nutrient Management Act
O.Reg. Ontario Regulation
O2 Oxygen
P Phosphorous
PSA Pressure Swing Adsorption
Ravensview Ravensview Wastewaster Treatment Plant
ACRONYMS & ABBREVIATIONS
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Acronyms/Abbreviations Definition
RDT Rotary Drum Thickeners
RNG Renewable Natural Gas
SSO Source-Separated Organics
TAD Thermophillic Anaerobic Digestion
TPAD Temperature-Phased Anaerobic Digestion
TS Total Solids
UK Utilities Kingston
VS Volatile Solids
VSD Volatile Sludge Destruction
WAS Waste Activated Sludge
WWTP Wastewater Treatment Plant
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LIMITATIONS OF REPORT This report and its contents are intended
for the sole use of Utilities Kingston and their agents. Tetra Tech
Canada Inc. (Tetra Tech) does not accept any responsibility for the
accuracy of any of the data, the analysis, or the recommendations
contained or referenced in the report when the report is used or
relied upon by any Party other than Utilities Kingston, or for any
Project other than the proposed development at the subject site.
Any such unauthorized use of this report is at the sole risk of the
user. Use of this document is subject to the Limitations on the Use
of this Document attached in the Appendix or Contractual Terms and
Conditions executed by both parties.
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1.0 INTRODUCTION
1.1 Project Background
Tetra Tech Canada Inc. (Tetra Tech) was retained by Utilities
Kingston (UK) to undertake the review and assessment of options, or
strategies, for enhancing biogas generation and managing biosolids
production at the Ravensview and Cataraqui Bay wastewater treatment
plants (WWTPs) in Kingston, Ontario. UK is a multi-utility provider
that is wholly owned by the City of Kingston (the City). The
purpose of the assignment is to develop a long-term,
environmentally sustainable and cost effective biosolids management
program that responds to current and future program challenges.
Since this would entail establishing a strategy comprised of
integrated systems at, potentially, multiple facilities and
locations, UK decided that the study would proceed as a Master Plan
conducted in accordance with the requirements of the Municipal
Engineers Association (MEA) Class Environmental Assessment (Class
EA) document.
Given developments in Ontario regarding: the consideration of
wastes as resources within the context of a circular economy; the
more effective management of source-separated organics (SSO) with
the objective of eliminating the landfilling of these materials and
the identification of opportunities for the generation and
utilization of renewable natural gas (RNG), UK defined the scope of
the study to include alternative systems that would entail the
co-digestion of biosolids and SSO collected by the City. In
addition, and further to the interest in considering co-digestion
systems, UK identified the Knox Farm property as a prospective
centralized location which would accept raw feedstocks, i.e.,
wastewater sludge from the two WWTPs, as well as SSO and leaf and
yard (L&Y) waste, transported from the two WWTPs and via SSO
and L&Y waste collection vehicles from sources within the City
of Kingston.
The study is comprised of three components. The first entailed
the completion of a preliminary assessment of alternative
technologies and processes to identify a short list for further
investigation. The second component has entailed the completion of
a detailed assessment of the short-listed technologies and
processes, including a financial feasibility evaluation of biogas
utilization. This second component is the subject of this report.
The third component will entail the completion of the Master Plan
in compliance with the MEA Class EA requirements and will be
undertaken subject to the results of the Detailed Assessment.
The analytical work undertaken by Tetra Tech in Component 1 of
the Study (the Preliminary Assessment) comprised:
The review and documentation of the existing operations at the
Ravensview and Cataraqui Bay WWTPs.
A comparative evaluation of relative “advantages” and
“disadvantages” of technologies and processesassociated with the
pre-treatment, treatment, stabilization, and management of
biosolids together with theco-digestion of biosolids and SSO. This
entailed an evaluation of alternatives in the following
categories:
− Sludge pre-treatment including: thickening; hydrolysis;
conditioning. and stabilization.
− Solids stabilization including: digestion, co-digestion,
post-treatment/composting, chemical stabilization;and thermal
stabilization.
− Biogas utilization including: on-site combined heat and power;
boilers; vehicle fuel station(s); local or regional natural gas
pipeline injection, and fuel cell technology.
− Dewatering including: centrifuge, belt-filter press, drying
beds, rotary vacuum filters, and enhanced solar.
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− Side-stream treatment including the struvite recovery and
ANAMMOX recovery processes.
− Biosolids management including: land application, landfill,
and utilization as construction material.
Identification of a recommended “short list” of alternative
technologies/systems for more-detailed assessment.
The results of this work were documented in the Preliminary
Assessment Report Issued for Use in April 2018, which identified
the following field of technologies to be further investigated:
Table 1-1:Further Investigated Technologies Categories
Technologies
Sludge Pre-Treatment 1. Thickening2. Biological Hydrolysis
Solids Stabilization 3. Anaerobic Digestion4. Co-digestion at
Ravensview (including SSO)5. Co-digestion at Cataraqui Bay
(including SSO)
Biogas Utilization 6. Microturbines7. Reciprocating Engines8.
On-Site Boiler9. Off-Site Vehicle Fueling
Dewatering 10. Centrifuge11. Belt-Filter Press
Biosolids Management 12. Cake/Slurry Land Application
The results of the second study component, the Detailed
Assessment of technologies and processes, are documented in this
report.
1.2 Detailed Assessment Approach and Methodology
The scope of the work undertaken for the subject Detailed
Assessment included:
Evaluation of existing wastewater treatment facility data
including plant capacity, population served, annualinfluent and
treated effluent, natural gas consumption, biogas generated, and
electricity consumption.
Scenario development of options for improving biogas generation
and quality, while decreasing biosolidsmanagement requirements for
UK.
Overview of potential end-use options for biogas and
biosolids.
Business case development and cost benefit analysis for each
developed scenario.
Review of funding opportunities available to UK.
The outcome of this Detailed Assessment is to develop a
framework for a UK Master Plan. Key factors for success include
determining viable end-use options for biogas and biosolids based
on current market and incentive programs, as well as cost benefit
analysis for capital and operating expenditures.
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2.0 DESCRIPTION OF EXISTING CONDITIONS
2.1 The Study Area The City of Kingston is located on the
eastern side of Lake Ontario and is home to 161,175 residents in
the metropolitan area with 123,798 residents within the city,
according to the 2016 Census. The city’s wastewater collection
system is split among three regions and services an approximate
area of 8,300 ha. The three regions include Kingston West, Kingston
Central, and Kingston East with an estimated 90% of the population
evenly divided between Kingston West and Kingston Central.
2.1.1 Cataraqui Bay Wastewater Treatment Plant The Cataraqui Bay
WWTP located at 409 Front Street was constructed in 1962. The
facility was upgraded in 2002 and is currently undergoing a major
expansion to increase plant capacity, improve the quality of
treated wastewater and upgrade equipment. Cataraqui Bay receives
wastewater, sanitary and extraneous flow from the Kingston West
region. The system operates under Environmental Compliance Approval
(ECA) Number 2144-87TJYB.
The upgrades currently under construction at the site will
increase capacity from 38,800 to 55,000 m3 per day. This expansion
is expected to be completed by 2020 and is based on the outcome of
the revised Sewage Infrastructure Master Plan finalized in 2010.
The upgrade work includes an expansion of the plant’s headworks and
primary clarifiers, replacement of the secondary treatment system,
electrical and instrumentation upgrades, and site-wide building and
process improvements.
The four-year construction project began in October 2016.
The upgrades include:
Phase 1: Increasing the plant’s wastewater treatment capacity
from the current 38,800 m3 per day to 55,000 m3 per day (average
flow), which Includes the redirection of the King-Portsmouth
Pumping Station to the CataraquiBay WWTP by 2020.
Phase 2: Increasing the Plant’s wastewater treatment capacity to
68,000 m3 per day (average flow). Projectedto be online by
2036.
Table 2-1: Existing and Upgraded Treatment Technology Treatment
Component Existing Upgraded
Liquids Train Technology
Preliminary Treatment
Preliminary treatment consists of two manually-cleaned aerated
grit tanks, followed by two mechanically-cleaned bar screens (bar
screens will be replaced by perforated plate fine screens).
The two steps of the existing process will be reversed so that
screening will occur before grit removal.
Primary Treatment
Influent enters primary settling tanks. Primary effluent passes
through aeration tanks.
Primary treatment tanks will be extended into the aeration tanks
to allow for the additional hydraulic and treatment capacity.
Performance will be enhanced through chemically enhanced primary
treatment.
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Treatment Component Existing Upgraded
Secondary Treatment
Influent passes into secondary clarifiers where it is treated
through a conventional activated sludge (CAS) process. Secondary
sludge is combined with primary effluent and is aerated to promote
biological growth before being passed through a final clarifier to
remove sludge.
Primary effluent will be directed to the biologically aerated
filter (BAF) system. The BAF process uses submerged media and
aeration to promote the growth of biomass in order to achieve BOD
removal, TSS removal, and nitrification. The BAF facility also has
a chemical treatment system for alkalinity adjustment.
Disinfection
Secondary effluent passes into a chlorine contact tank, where
chlorine is added to the water. Residual chlorine is removed
through a dechlorination system before discharge.
Two existing secondary clarifiers will be converted into
chlorine contact tanks.
Dechlorination Calcium thiosulfate is injected into the plant
effluent water downstream of the chlorine contact tank to
dechlorinate.
A new dechlorination room will be constructed, however, the
process will stay the same.
Solids Train Technology
Sludge Thickening
The solids train consists of rotary drum thickeners, anaerobic
digesters, sludge holding tanks, dewatering centrifuges, open
sludge drying bed, and an open biosolids storage pad. Waste
activated secondary sludge is pumped to the Rotary Drum Thickeners
RDT) before being pumped to the digesters.
The following processes will be used: Dedicated thickening
process using a
gravity thickener. Co-thickening of the backwash residuals
(back-up operation).Two gravity thickener tanks will be
retrofitted from the existing secondary clarifiers. Existing
secondary clarifiers will be offline so there will be no secondary
sludge. Backwash residuals from the BAF process will be thickened
using two gravity thickeners retrofitted from two existing
secondary clarifiers. Thickened BAF backwash resduals will be
pumped to the two existing RDTs before being sent to the digesters.
During certain periods of time of construction, the BAF will be
online and the RDTs will be offline for electrical upgrades. During
this time period the BAF backwash residuals will be
co-thickened.
Anaerobic Digestion
Sludge is anaerobically digested.
Sludge is anaerobically digested. Digester expansion, which was
originally recommended in the 2012 Class EA, will be deferred, as
the existing digesters have capacity for short-term needs. New
digestion capacity is not expected to be needed until 2029.
Upgrades to the existing digester mixing systems and heat
exchangers will be deferred form upgrades to coincide with a future
digester cleanout, re-gas proofing and re-roofing project.
Dewatering and Biosolids Storage
Dewatering Biosolids are dewatered using centrifuges and a
biosolids drying bed.
A new Dewatering and Biosolids Storage Facility will be
constructed. Digested sludge will be pumped to the new centrifuges
by new rotary lobe sludge transfer pumps.
Biosolids Storage
Dewatered biosolids are stored onsite at the sludge storage pad
when land application is not permitted.
The new facility will store dewatered cake in two buildings and
will have capacity for 240 days of biosolids cake storage.
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Treatment Component Existing Upgraded The new biosolids cake
storage facility (similar to Ravensview WWTP) will be constructed.
A key difference from the Ravensview WWTP is that the cake will be
moved by gravity, not pumped. This will result in a different
consistency than is currently seen at Ravensview.
Digester Gas Utilization
Currently, digester gas is collected from each digester and the
sludge holding tank, is compressed, and injected back into the
digester for mixing. Excess gas is either routed to the boilers or
to the waste gas flare.
The existing mixing system and waste flare system will remain
unchanged. A new digester gas booster will be provided to boost the
digester gas pressure to the boilers at the BAF facility.
The upgrades to Cataraqui Bay are summarized in the following
major components:
Demolition of the existing Septage Receiving Station;
A new and expanded Headworks Building to house two fine screens,
two vortex grit tanks, and their auxiliarysystems;
Connection of the primary clarifiers and aeration tanks to
create four new retrofitted primary clarifiers;
A new BAF Facility, which will consist of:
− Six BAF cells;
− A Primary Effluent Pumping Station;
− Two BAF backwash residual tanks;
− Process Equipment Space; and
− Administration and laboratory functions.
An expanded chlorine contact tank.
Diffuser upgrades for the existing two outfalls.
A new Dewatering and Biosolids Storage Facility to house two
centrifuges and two biosolids bunkers.
A new prefabricated centrate pumping station.
Two new gravity thickeners to treat BAF backwash residuals
retrofitted from the existing secondary clarifiers.
An expanded Chemical Building to house new chlorinators.
A retrofitted Dechlorination Building to house chemical storage
and dosing equipment.
A new electrical substation and backup generator located close
to the site entrance.
Two new tunnels to connect to the BAF Facility and Dewatering
and Biosolids Storage Facility.
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Decommissioning of Plant C East and the Plant D secondary
clarifiers1.
The upgraded treatment process at Cataraqui Bay is illustrated
in Figure 2-1.
Figure 2-1: Upgraded Cataraqui Bay Treatment Flow Diagram
Biological Aerated Filter
2.1.2 The Ravensview Waste Water Treatment Plant The Ravensview
WWTP, located at 947 County Road #2, was constructed in 1957 as the
first waste water treatment plant in Kingston. The plant was
upgraded in 1974, in 1993, and most recently between 2006 to 2009
(with a $115,000,000 capital project). The plant is designed to
process 95,000 m3 of waste per day, primarily generated from the
Central to East regions of the City.
The current waste water treatment process is illustrated in
Figure 2-2.
Figure 2-2: Ravensview Waste Water Treatment Flow Diagram
Backwash
1 Cataraqui Bay Wastewater Treatment Plant Upgrades Design
Report, January 2016
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2.1.3 The Cana Wastewater Treatment Plant The CANA WWTP was
constructed in the early 1970’s for the CANA Home-Building
Cooperative. In 1991, the City acquired the facility and it is
currently maintained and operated by UK. Cana was upgraded to an
SBR, completed in 2018 and currently meets all requirements for
discharge. Sludge from Cana is currently transported to Ravensview
for digesting. The CANA WWTP is not considered a viable option for
enhancement.
2.2 Existing B iosolids Management Processes
Both Cataraqui Bay and Ravensview have undergone changes to
their respective processes from the time of commissioning. For the
purposes of this review, the following descriptions outline the
processes for the respective facilities that match the period of
background data that is presented in Sections 3.2.2, 3.2.3, and
3.2.4.
The current process at both plants is comprised of primary
settling tanks, secondary settling tanks, digesters, primary
settling, biological treatment, secondary setting, thickening,
digestion, biosolids dewatering and storage.
For biological treatment, both facilities use the BIOSTYR®
process, which is an up-flow submerged media BAF. As an attached
growth process, BIOSTYR is carried out in a series of individual
cells containing submerged buoyant media, which provides surface
area for microorganisms to attach and grow. Extra activated sludge
falls off of the media and is filtered and removed as waste
activated sludge (WAS).
The WAS is then pumped to the Digesters for stabilization and
methane production.
For the purpose of describing the biosolid characteristics, for
Ravensview and the pre-design of Cataraqui Bay, the following will
be detailed:
Ravensview, two mesophilic, one thermophilic digester and one
storage tank.
Cataraqui Bay, two mesophilic digesters plus one storage
tank.
Dewatering.
Storage.
2.2.1 Biosolids Characteristics, Quantities and Projections
2.2.1.1 Characteristics Wastewater biosolids are the residual
material from the sludge treatment works after the sludge has been
stabilized in the digestion process. Biosolids primarily consist of
nutrients, organic matter, and micronutrients, such as copper and
zinc. They may also contain trace amounts of other elements, such
as arsenic, lead, and mercury.
Table 2-2 Cataraqui Bay and Ravensview WWTP Biosolids
Characteristics” summarizes biosolids characteristics from the UK’s
two WWTPs compared with typical values in the MECP Design
Guidelines (2008) and Metcalf and Eddy (2003). Most of the
characteristics for UK’s biosolids are comparable to typical values
in design guidelines and literature.
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Table 2-2 Cataraqui B ay and Ravensview WWTP Biosolids
Characteristics
Biosolids Type Parameters Cataraqui Bay WWTP
Ravensview WWTP Typical Design Guidelines
Raw Sludge
TS% 3.82 4.15 2-6.5 1
Ave. 4.0
VS% 82.8 68.2 60
TS (mg/L) 38,239 n/a
VS (mg/L) 31,497 n/a
Digested Sludge
TS% 2.32 2.10 2-6 1
Ave. 4.0
VS% 64.9 49.1 45
TS (mg/L) 21,489 n/a
VS (mg/L) 13,936 n/a
Dewatered Cake
TS% 14.0 28.6 15-30 1
VS% 64.5 48.0
TS (mg/L) 140,146 n/a
VS (mg/L) 90,631 n/a
DETAILED ASSESSMENT REPORT FILE: 704-SWM.SWOP03442-01 | JULY
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Sources: Cataraqui Bay and Ravensivew WWTP Annual Reports, 2015
– 2017. Notes: 1 All values are yearly average from monthly data
between 2015 and 2017. Design Guidelines for Sewage Works, MECP
(former MOECC) (2008)
The Ontario Nutrient Management Act (NMA) (O.Reg. 267/03) was
enacted to minimize the risk to public health and the environment
when non-agricultural source materials (NASM), including sewage
biosolids, are applied to land. Under the NMA, WWTPs are considered
to be generators of Category 3 NASM. Biosolids generated from
Category 3 NASM are required to meet CM2 criteria for regulated
metals and CP1 or CP2 criteria for pathogens as set out in the
Regulation when applied to agricultural land as a nutrient.
Table 2-3 summarizes the concentrations of 11 metals of concern
regulated under NMA in biosolids generated from Cataraqui Bay WWTP
and Ravensview WWTP as compared with the quality requirements for
NASM CM1 and CM2 biosolids.
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Table 2-3 Cataraqui Bay and Ravensview WWTP Biosolids Metal
Content as Compared to NMA Standards
Element Cataraqui Bay WWTP
(2015 2016)
Ravensview WWTP (2015 2016)
CM1 NASM (1) CM2 NASM (2)
Arsenic 2.4 4.8 13 170
Cadmium 1.0 0.8 3 34
Chromium 53 75 210 2,800
Cobalt 1.6 4.5 34 340
Copper 482 747 100 1,700
Lead 16 51 150 1,100
Mercury 0.8 0.9 0.8 11
Molybdenum 7.1 8.0 5 94
Nickel 20 24 62 420
Selenium 3.6 4.3 2 34
Zinc 657 660 500 4,200
Notes: All units are expressed as mg per kg of total solids, dry
weight. Bolded values indicate values exceeding CM1 NASM limits.
Column 3 of Table 1 of Schedule 5 Regulated Metal Content of NASM
under Nutrient Management Act, 2002 (O. Reg. 267/03) Column 3 of
Table 2 of Schedule 5 under NMA, 2002 (O. Reg. 267/03)
Based on the data from 2015 - 2016, biosolids generated from
both plants are low in above regulated metal concentrations. These
biosolids can be used on agricultural land that meet the quality
criteria in a manner consistent with the practice acceptable under
the NMA. Biosolids from both plants meet the metal requirements for
Category CM1, with the exception of copper, mercury, molybdenum,
selenium and zinc (bolded) that requires management as CM2C. It is
important to ensure that the projected metal concentrations for
future productions also remain below the maximum concentrations
stated in the regulations.
In addition to metal content, it may also be beneficial to
review additional requirements for biosolids quality related to
pathogens prior to land application. The pathogen content of NASM
that is sewage solids or contains human body waste (CP2 Pathogen
Criteria) as compared with the pathogen analysis from plant
biosolids samples is summarized in the table below.
Table 2-4 Cataraqui Bay WWTP and Ravensview WWTP Biosolids
Pathogen Content as Compared to NMA Standards
Pathogen Cataraqui Bay WWTP
Ravensview WWTP CP1 NASM 1 CP2 NASM 2
E. coli 9,183 CFU/g 22,203 CFU/g3 1,000 CFU per gram of total
solids, dry weight
2,000 CFU per gram of total solids, dry weight
Salmonella Data not available Data not available 3 CFU or MPN
per 4 gram of total solids, dry weight
n/a
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Pathogen Cataraqui Bay WWTP
Ravensview WWTP CP1 NASM 1 CP2 NASM 2
Giardia Data not available Data not available No detectable
level in 4 gram of total solids, dry weight
n/a
Cryptosporidium Data not available Data not available No
detectable level in 4 gram of total solids, dry weight
n/a
Notes: 1CFU refers to colony forming units. This methodology is
used for determining number of coliform counts in a given sample.
2Column 3 of Table 2 of Schedule 6 Pathogen Content of NASM (O.
Reg. 267/03) 2Column 3 of Table 3 of Schedule 6 Pathogen Content of
NASM (O. Reg. 267/03) 3Due to repairs to the Thermophilic and one
Mesophilic digesters this does not represent expected quality
2.2.1.2 Quantities The plant flow and sludge data were obtained
from Cataraqui Bay WWTP and Ravensview WWTP Annual Reports for the
years 2015 to 2017, and are summarized in Table 2-5 and Table 2-6
below.
Table 2-5 Historical Annual Effluent and Biosolids Quantities in
Cataraqui Bay WWTP (2015 – 2017)
Cataraqui Bay 2015 2016 2017 Average
Effluent Volume (m3/yr) 9,527,449 9,962,485 10,965,006
10,151,647
Raw Sludge Volume (m3/yr) 23,332 25,117 25,267 24,572
Volume of raw sludge
generated per volume of effluent
L/m3 2.4 2.5 2.3 2.4
Dewatered Cake Volume (m3/yr) 4,086 4,358 3,734 4,059
Sources: Cataraqui Bay WWTP Annual Report Data, 2015 - 2017
Table 2-6 Historical Annual Effluent and Biosolids Quantities in
Ravensview WWTP (2015 – 2017)
Ravensview 2015 2016 2017 Average
Effluent Volume (m3/yr) 21,972,284 20,609,884 31,499,468*
21,291,084
Raw Sludge Volume (m3/yr) 52,896 55,075 61,106 53,986
Volume of raw sludge generated
per volume of effluent
L/m3 2.4 2.7 1.9* 2.5
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Ravensview 2015 2016 2017 Average
Dewatered Cake Volume (m3/yr) 4,999 3,816 5,577 4,408
Sources: Ravensview WWTP Annual Report Data, 2015 – 2017 Notes:
* The flows in 2017 were abnormally larger than previous years due
to high lake level in 2017 summer. Effluent value in 2017 will
be
treated as an outlier and excluded in the calculation for
projections.
According to Table 2-5 and Table 2-6, the volume (L) of raw
sludge generated per volume (m3) of treated wastewater are 2.4 L/m3
and 2.5 L/m3 for Cataraqui Bay WWTP and Ravensview WWTP,
respectively. These values are close to, but below the typical
value of 3.2 L/m3 suggested by MECP Guidelines for a primary
sedimentation plant with phosphorus removal. The total solids (TS%)
of raw sludge are 3.82% and 4.15% for Cataraqui Bay WWTP and
Ravensview WWTP, respectively. For the purposes of this analysis,
it was assumed that TS% of raw sludge will be the same in the
future and the same values of TS% were used for sludge projection.
It should be noted that the two plant processes combined sewer and
extraneous flow sources, thereby explaining the lower raw sludge
generation.
These values were used as the basis for the future biosolids
projections up to year 2037.
2.2.1.3 Projections Sludge production was estimated based on
population growth in the City of Kingston (Statistics Canada) and
typical human deposit (solids) generated per capita (g/ca/day), in
conjunction with the sludge data from the WWTP Annual Reports for
2015 to 2017, inclusive.
City of Kingston’s population grew slowly between 2011 and 2016,
increasing by 1.03% from 114,928 to 117,660. For the purposes of
the analysis, it was assumed that the population growth trends for
the City would follow the same rate as in the previous intercensal
period to complete the projections from 2022 to 2037. Serviced
population was estimated based on the City of Kingston wastewater
collection system serviced by the two WWTPs. Cataraqui Bay WWTP
services Kingston West (3,953 ha, 44,400 POP), which accounts for
38% of the total population, and Ravensview WWTP collects
wastewater flow from Kingston Central (2,919 ha, 54,600 POP) and
East (1,386 ha, 10,200 POP), which accounts for 55% of the City’s
total population. Additionally the Cana WWTP, located north of the
Highway 401, services the Cana subdivision, which will not be
covered in this detailed analysis.
Future biosolids production, utilizing the projected serviced
population and quantity of sludge generated from each of the WWTPs,
is summarized in Table 2-7 below.
Table 2-7 Projected Annual Biosolids Production in Cataraqui Bay
WWTP up to Year 2037
Year Serviced Population
Raw Sludge Dewatered Cake
Total Volume
Production Concentration
Total Mass*
Total Volume
Production Concentration
Total Mass**
(m3/yr) (g/cap.d) (kg/yr) (m3/yr) (g/cap.d) (kg/yr)
Collected Data
2015 44,200 23,332 54 877,658 4,086 33 528,237
2016 44,410 25,117 57 926,990 4,358 36 586,002
2017 44,621 25,267 62 1,015,571 3,734 36 585,120
2022 45,692 25,278 58 966,993 4,177 35 582,717
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Year Serviced Population
Raw Sludge Dewatered Cake
Total Volume
Production Concentration
Total Mass*
Total Volume
Production Concentration
Total Mass**
(m3/yr) (g/cap.d) (kg/yr) (m3/yr) (g/cap.d) (kg/yr)
Projected Data
2027 46,788 25,885 58 990,199 4,277 35 596,701
2037 49,061 27,142 58 1,038,296 4,485 35 625,684
Notes: The average undigested sludge solid concentration over
the three years (2015-2017) was 58 g/cap.d, which is below the
typical value of 100 g/cap.d for CAS w/P removal suggested by MECP
Sewage Works Design Guideline (2008). The average digested sludge
solid concentration over the three years (2015-2017) was 35
g/cap.d, which is below the typical value of 68 g/cap.d for CAS w/P
removal suggested by MECP Sewage Works Design Guideline (2008).
Raw sludge and dewatered cake production (in mass) were
calculated based on undigested sludge and digested solids
production concentration per capita multiplied by the projected
population of the same year. It should be noted that the average
undigested sludge production concentration per capita of 58 g/cap.d
was far below the typical value of 100 g/cap.d for a CAS process as
suggested in the MECP Guidelines. As expected, the average digested
solids production concentration per capita of 35 g/cap.d was also
below the typical value of 68 g/cap.d.
Figure 2-3 Projected Biosolids Production in Cataraqui Bay WWTP
up to Year 2037
Note: Raw Water Volume is at +/- 2% solids and Dewatered Cake
Volume is +/- 25% solids
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Table 2-8 Projected Annual Biosolids Production in Ravensview
WWTP up to Year 2037 Year Serviced
Population Raw Sludge Dewatered Cake
Total Volume
Production Concentration
Total Mass*
Total Volume
Production Concentration
Total Mass**
(m3/yr) (g/cap.d) (kg/yr) (m3/yr) (g/cap.d) (kg/yr)
Collected Data
2015 64,508 52,896 100 2,354,531 4,999 68 1,601,081
2016 64,814 55,075 100 2,365,725 3,816 68 1,608,693
2017 65,123 61,106 100 2,376,972 5,577 68 1,616,341
Projected Data
2022 66,685 55,673 100 2,434,016 4,935 68 1,655,131
2027 68,286 57,009 100 2,492,429 5,054 68 1,694,851
2037 71,603 59,778 100 2,613,493 5,299 68 1,777,175
Notes: Plant effluent and raw sludge volume in 2017 was treated
as an outlier due to high lake level in 2017 summer, and excluded
in the calculation for projections. Data are not available for
Ravensview WWTP. Undigested sludge solid concentration of 100
g/cap.d and digested sludge solid concentration of 68 g/cap.d (CAS
w/P removal) were used for projections (MOECC Sewage Works Design
Guidelines, 2008).
The same methodology was used to project raw sludge and
dewatered cake production for Ravensview WWTP. Typical undigested
sludge production concentration of 100 g/cap.d and digested solids
production concentration of 68 g/cap.d were used for the
calculations.
The projected annual biosolids production from the two plants to
2037 (Table 2-9) were used as a basis for developing and reviewing
the various alternative biosolids management options.
Figure 2-4 Projected Biosolids Production in Ravensview WWTP to
Year 2037
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
3,500,000
4,000,000
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
2015 2016 2017 2022 2027 2037
Bio
solid
s M
ass
(kg/
yr)
Bio
solid
s Vo
lum
e (m
3/yr
)
Year
Raw Sludge Volume Dewatered Cake Volume Raw Sludge Mass
Dewatered Cake Mass
(Dashed)
(Dashed)
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Table 2-9 Total Annual Biosolids Production in Year 2037
Facility Raw Sludge Cake
Volume (m3/d) Mass (kg/d) Volume (m3/d) Mass (kg/d)
Cataraqui Bay 74 2,957 12 2,004
Ravensview 164 7,094 15 5,810
Total 238 10,051 27 7,814
2.2.2 Existing Biosolids Treatment Capacity
2.2.2.1 Cataraqui Bay Table 2-10 summarizes the treatment
capacities of the existing sludge treatment components in Cataraqui
Bay WWTP.
Table 2-10 Biosolid Process Design Parameters in Cataraqui Bay
WWTP Unit Size/Capacity Description
WAS Holding Tanks (four tanks)
230 m3 (each) 920 m3 (total)
The two WAS holding tanks with two positive displacement blowers
providing air to the fine bubble membrane diffusers within
the tank. Two WAS sludge pumps are rated at 34.7 L/s each.
Rotary Drum Thickener (two thickeners)
125 m3/hr (each) 1,250 m3/d (total)
Currently both thickeners are operated approximately five hours
per day, seven days per week.
WAS is thickened in rotary drum thickeners prior to being pumped
to digesters.
Thickened WAS Holding Tanks
(two tanks)
590 m3 (each) 1,180 m3 (total)
With two TWAS pump each rated at 600 m3/hr.
Primary Digesters (Digester No. 3)
3,060 m3 Hydraulic retention time in primary digester is 34
days.
Secondary Digester (Digester No. 2)
1,620 m3 With capability of operating as a primary digester.
Volatile destruction is 54% in secondary digester.
Equipped with two digested sludge pumps each rated at
12.6L/s
Digested Sludge Holding Tank
(Digester No. 1)
1,540 m3
Dewatering Centrifuge (one unit)
10.6 L/s (638 L/min)
Centrifuge is operated 8 hours per day, 2 to 3 days per week.
Historically has dewatered digested biosolids to 16% TS with
99%
of solids capture.
2.2.2.2 Ravensview Table 2-11 summarizes the design parameters
of key sludge process components in the Ravensview WWTP.
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Table 2-11 Biosolid Process Design Parameters in Ravensview WWTP
Unit Size/Capacity Description
Mesophilic Digesters (two tanks)
2,465 m3 (each tank) 4,930 m3 (total)
Both tanks are equipped with four vertical draft tube mechanical
mixers. Tanks are heated by continuous sludge recirculation
through hot water tube type heat exchangers. The two primary
clarifiers can be operated in series or in parallel,
and normally in-series mode operation. Three sludge circulation
pumps each rated at 30L/s.
Secondary Digester (one tank)
3,700 m3 Not heated or continuously mixed. Equipped with
external pump recirculation system used to maintain sludge
consistency and
minimize solids accumulation. Two sludge transfer pumps each
rated at 11 L/s.
Thermophilic Anaerobic Digester
(one tank)
2,465 m3 Primary digester with the ability to conduct
temperature phased anaerobic digestion.
Two sludge circulation pumps each rated at 132 L/s.
Dewatering Centrifuge (two units)
9.1 L/s (each) (546 L/min)
1,092 L/min (total)
Historically has dewatered digested biosolids to 30% TS.
2.2.3 Biosolids Storage Requirements Biosolids storage
requirements were developed based on providing 180 days of storage
for biosolids generated at Cataraqui Bay WWTP and Ravensview WWTP.
Based on Ontario Regulation 267/03, restricted land application
applies from December 1 to March 31 (4 months) when the ground is
covered by snow or frozen. Provision of 180 days of storage would
allow sufficient storage for the restricted period, while providing
some buffering capacity in the event that land application is not
possible outside the restriction period. The NMA requires storage
capacity for 240 days. This is why Ravensview WWTP includes 180
days storage pus the intent to landfill or direct apply to fields
in the event storage is full. The UK management plan includes
contingency to landfill if storage capacity is exceeded.
The design biosolids storage requirements for the two plants are
provided in Table 2-12. Biosolids generation rates were developed
based on standard mesophilic anaerobic digestion. Pre-treatment and
stabilization processes will have an impact on the biosolids
generation rate and will affect storage requirements and
options.
Table 2-12 Biosolids Storage Requirements in Year 2037 Standard
Anaerobic Digestion Cataraqui Bay WWTP Ravensview WWTP
Biosolids Mass 2,004 kg/d 5,810 kg/d
Generated Cake Volume 12 m3/d 15 m3/d
Biosolids Storage Requirements (1) 2,160 m3 2,700 m3
Notes: The Nutrient Management Act stipulates 240 days of
required biosolids storage for agricultural uses.
Storage facilities for storage of biosolids cake is provided at
the sites of Cataraqui Bay WWTP and Ravensview WWTP. A review of
existing storage capacities on site for the two plants is provided
in Table 2-13. The existing storage facilities on-site can provide
sufficient capacities for sewage generated biosolids to 2037.
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Table 2-13 On-site biosolids storage capacities at Cataraqui Bay
and Ravensivew Facility Unit Size/Capacity
Cataraqui Bay WWTP New Enclosed Sludge Drying Beds 5,125 m3
Ravensview WWTP Enclosed Cake Storage Facility 6,000 m3
2.3 Existing Biogas Management Processes
2.3.1 Biogas Characteristics, Quantities and Projections
Ravensview’s total biogas flow (generator, flare, and boiler)
varies from about 1,000 to 4,000 m3 per day (or 25 to 100 cfm) and
is highly variable with consistently more biogas collected in the
spring of the year. Figure 2-5 summarizes historic biogas flow in
2013 to 2016 from the Ravensview WWTP. The biogas chemistry data
showed that Ravensview biogas has excellent concentration of
methane, with no oxygen or nitrogen levels. The data provided is 10
to 12 years old. Siloxane levels were found to be very high and
considering the age of these results Tetra Tech recommends
re-testing all gas chemistry.At this time no further samples have
been taken as the digesters at Ravensview have been down.
Figure 2-5: Ravensview Digester Gas Production
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Cataraqui Bay’s total biogas flow (flare and boiler) varies from
about 1,000 to 3,000 m3 per day (or 25 to 75 cfm) and is highly
variable with consistently more biogas collected in the spring of
the year. Figure 2-6 summarizes historic biogas flow in 2013 to
2016 from Cataraqui Bay WWTP.
Figure 2-6: Cataraqui Bay Digester Gas Production
The biogas chemistry data showed that Cataraqui Bay’s biogas has
an excellent concentration of methane, with no oxygen or nitrogen
levels. The data provided is three years old. Siloxane levels were
found to be very low so Tetra Tech recommends retesting to confirm
the siloxane levels.
With the planned upgrade/enhancements of the Cataraqui Bay
digesters, it is expected that the biogas output may change. With
the addition of SSO, it is expected that the biogas
characterization will change and that O2 and N2 levels will
increase. Further, the addition of SSO may introduce aromatics to
the biogas.
(http://www.biogas-renewable-energy.info/biogas_composition.html)
As will be shown in Section 3, it is expected that some of the
technology options will increase the production of biogas, and
hence increase the amount of methane that may be available for
use.
2.3.2 Existing Biogas Treatment Capacity Cogeneration of
electricity and heat is currently employed at Ravensview WWTP but
not at Cataraqui Bay WWTP. Both facilties also dispense generated
gas for boilers and flares. This technique to convert biogas to
energy is very common at WWTPs throughout Canada and the USA
because it reduces the amount of electricity that must be purchased
from the grid to operate the WWTP. It is presumed that this
self-generation of electricity reduces costs because the cost of
self-generated electricity is less compared to purchasing
electricity from the grid. This will be reviewed by Utilities
Kingston. In addition, the heat from the generation equipment can
be harnessed and employed to keep the WWTP digesters operating at
peak temperature, especially in the winter months. Additional heat
may
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also be recovered for use in building heating and meeting other
on-site needs. Any excess gas that cannot be used for either
electrical production or for heat can otherwise be flared.
2.4 Pre-Selected Treatment Technologies
Cleaning and compression of biogas into RNG has become
commonplace in the USA and Canada. Several vendors of gas cleaning
equipment are based in Canada, such as Greenlane (BC), Xebec
(Quebec), and others. In addition, several USA equipment suppliers
deliver their equipment to Canada such as BioCNG. Technologies for
cleaning biogas into RNG are shown in Figure 2-7.
Bio Gas
PSA – Pressure Swing Adsorption
Membrane Separation
Scrubbing
Figure 2-7: Biogas Treatment Technologies
There are four types of biogas treatment that can be
contemplated for this application. Pressure Swing Adsorption (PSA),
Membrane Separation, Water Scrubbing, and Amine Scrubbing.
2.4.1 PSA PSA uses a batch of vessels that increase the pressure
of the biogas to a point where most non-methogenic compounds (CO2,
H2S, Siloxane O2, and aromatics) are adsorbed into a medium and the
“cleaned” methane is expelled. When the pressure is reduced, the
adsorped compounds are released and expelled. There are several
types/versions of PSA systems depending on the manufacturer. PSA is
used in many applications including high and low flow
applications.
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Figure 2-8: Pressure Swing Adsorption
2.4.2 Membrane Separation Membrane separation is the application
of polymeric membranes to separate CO2 from methane as the biogas
is subjected to a vessel where the membrane has separate outlets
for each of the compounds. One problem is that the membrane can be
plugged by other compounds so the biogas is typically cleaned with
H2S removal via activated carbon and a water knockout is used prior
to entering the membrane chamber.
Figure 2-9: Membrane Separation
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2.4.3 Water Wash/Scrubbing The water wash scrubbing process is
similar to membrane separation as water is used to dissolve CO2.
The process is undertaken in two high and low pressurized vessels
where a membrane separates the two compounds in the dissolved
state. The process requires H2S and moisture pre-treatment similar
to that in membrane separation.
Figure 2-10: Water Wash
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2.4.4 Amine Scrubbing In this process Amine is used to
chemically react with CO2 and is adsorped. The methane is then
released. The process is undertaken in two towers where the reacted
amine and CO2 is heated in a separated tower to release the CO2 and
the amine is then recovered with an amine cooling system. Similar
to the above-noted processes, the biogas needs to be desulfered
prior to processing.
Figure 2-11: Amine Scrubbing
2.4.5 Recommended Process At this time it is difficult to assess
which process is most applicable. Furthermore, if the digesters are
modified or changed then the constituent compounds may be different
and, in some cases, may require pre-treatment for a specific
constituent. With the addition of SSO into the digestion process,
the output constituents may be different again. Given the
information that is available , including the anticipated flow
rates of biogas, versions of PSA may be the most cost beneficial
process and can be provided by most gas cleaning suppliers.
It should also be noted that Union/Enbridge (now Enbridge) may
offer to install the gas cleaning and compression equipment for
testing.
2.5 End-Use
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The end use for the RNG generated from the generating site was
initially considered to be CNG, with the alternative being either
to fuel a Natural Gas fleet, or to ship it to a consolidating
station. If done within Ontario, the initial objective was to
either offset the gas penalties for the gas distribution system
owned by the City, or to take advantage of green fuel credits, both
under the auspicies of the Ontario Cap and Trade legislation. This
objective became less likely with the current cancellation of the
Cap and Trade Legislation but may be resurrected with federal and
future provincial green fuel programs.
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At this time, the primary driver to attain carbon credits for
RNG is to inject the gas into a distribution network such as
Union/Enbridge (which are currently the suppliers of natural gas to
the two WWTPs). Union/Enbridge has indicated that gas can only flow
in one direction so the injected RNG must have enough consumptive
capacity downstream from the injection point. Based on information
provided by Union/Enbridge the following are the results of their
analysis of the pipelines.
Site 1: Ravensview WWTP 947 Hwy 2, Kingston, ON, K7L 4V1
(44°14'32.5"N 76°25'12.0"W):
− This pipeline does not have much flow during the summer.
Modelled takeaway capacity is 53 m3/hr at theroad on a 420 kPa
maximum operating pressure line. During the winter, it is expected
to be 3 or 4x flow.
− There is another higher pressure pipeline close to the St
Lawrence River which is 3.7 km away that Union/Enbridge has not yet
looked at.
Site 2: Cataraqui Bay WWTP 80 Sunny Acres Rd, Kingston, ON
(44°12'37.0"N 76°33'39.8"W):
− Inject into the 1210 kPa Union/Enbridge system at a delivery
pressure of 1140 kPa.
− Requires ~1.1km of 4” steel connecting pipe.
− Modeled low flow scenario is 283 m3/hr and again typically 3
or 4x during winter loads.
In either case, the recommendation is for the injected gas to be
wheeled where there are existing or yet to be established RNG
purchase programs, namely Quebec and British Columbia. For each of
these options there needs to be a connection to the Dawn Wells,
which then connects with TransCanada to each of the provinces.
Tetra Tech has communicated with both Fortis BC and Energir
(previously Gaz Metro) and have attained interest from both groups
to potentially purchase RNG generated from the UK facilities. In
both cases, the incentive for any agreement would be to have a
long-term established cash flow dependent on a range of gas flows.
Table 2-14, Below, shows the potential range for purchase
agreements.
Table 2-14, Potential Range for Purchase Agreements
Provider Rate Duration Transport to Dawn Other Transport
Total
Energir $18 first three years $14 thereafter per GJ
(higher rates negotiable)
negotiable $1 per GJ none Estimated $14 to $18 per GJ
Fortis $25 to $30 20 years $1 per GJ $4 per GJ $20 to $25 per
GJ
It should be noted that the range of purchase prices are
negotiable and would need to be clarified if and when UK makes a
decision on proceeding with the project.
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3.0 ALTERNATIVE BIOSOLIDS AND BIOGAS MANAGEMENT OPTIONS
3.1 Option 1 – Do Nothing
3.1.1 Description of Alternative Under Option 1, sludge
treatment, the current practice of processing sewage sludge
separately at the WWTPs will continue. Both primary sludge and WAS
are passing through thickening, mesophilic anaerobic digestion
(MAD), secondary digester settling and dewatering at Cataraqui Bay
WWTP (shown in Figure 3-1). Primary sludge and thickened backwash
solids are subject to temperature-phased anaerobic digestion
(TPAD), secondary digester settling and dewatering at Ravensiview
WWTP (shown in Figure 3-2).
Option 1 Schematic - Existing Mesophilic Anaerobic Digestion
(MAD) at Cataraqui Bay
Mesophilic
Digester
Mesophilic
Digester
Secondary
Digester Dewatering
Cake
Storage
MAD
Thickener
3
Biogas
1
4
2
Centrate
Cataraqui Bay
Sludge
Figure 3-1 Existing Solid Treatment Process at Cataraqui Bay
WWTP Option 1 Schematic - Existing Temperature Phased Anaerobic
Digestion (TPAD) at Ravensiview
Thermophilic
Digester
Mesophilic
Digester
Mesophilic
Digester
Secondary
Digester
Dewatering
Dewatering
Cake
Storage
Temperature Phased
Anaerobic Digestion
1
2
3
4
Biogas
Centrate
Ravensiew
Sludge
Figure 3-2 Existing Solid Treatment Process at Ravensview
WWTP
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3.1.2 Impact on Existing Facilities The following assumptions
and approaches were used to estimate biosolid production and biogas
generation:
1. Under all the other alternatives (Option 2-5), sludge
produced in the UK’s two WWTPs will be processed in one centralized
location.
2. Solids production and biogas yield estimates are calculated
based on mass balance for the entire solid treatment train,
consider the solid treatment process system boundary shown on
Figure 3-1 and Figure 3-2.
3. Flow fluctuations of the raw sludge production were not
considered in the estimation of sludge quantities.
4. Projected values of total sludge produced from both plants in
the year 2037, i.e., sludge volume, total solid loading, and
volatile solid loading, were used as the process input in all
options.
5. Raw sludge from Cataraqui Bay WWTP was assumed to consist of
50% primary sludge and 50% WAS (or Waste Thickened BAF sludge),
while sludge from Ravensview WWTP consists of primary sludge and
BAF backwash solids.
6. Estimation of cake biosolid production and biogas yield were
based on 15-day hydraulic retention time (HRT) in mesophilic
digestion phase for all digestion scenarios.
7. Based on plant historical data, convertible COD in volatile
solids (VS) of primary sludge and WAS were assumed to be 1.65 kg
COD/kg VS and 1.47 kg COD/kg VS, respectively. Convertible COD in
the blended sludge was calculated in proportion to the percentages
of primary sludge and WAS in the feedstock.
8. Based on industrial experience at similar facilities,
volatile sludge destruction (VSD) rates were assumed to be 40% for
conventional MAD, 50% for TPAD, and 54% for Biological Hydrolysis –
Anaerobic Digestion (BH-AD).Combined VSD was used to estimate VS
residual after digestion and biosolid production.
9. The methane (CH4) converted from COD under anaerobic
conditions is 0.4 L CH4/g COD = (25.29 L/mole)/(64 g COD/mole CH4).
Biogas flow was calculated based on 65% CH4 in the total gas
flow.
10. Nutrient mass loadings (i.e., nitrogen and phosphorus) of
the dewatering centrate produced under the current operation
condition at each plant were used as the baseline for evaluation.
It should be noted that Ravensivewhas a larger volume of dewatering
centrate with lower concentration of nutrients.
The “Do Nothing” option is presented solely to provide a
comparative baseline for the evaluation of alternative options and
is not considered a viable strategy for this study.
Table 3-1 Estimated Biosolids Production and Biogas Generation
in the Year 2037 Cataraqui Bay Ravensview Total
Feedstock
Sludge Volume (m3/d) 74 164 238
TS Loading (kg/d) 2,957 7,094 10,051
VS Loading (kg/d) 2,448 4,837 7,285
Biosolids
Biosolids (m3/d) 12 15 27 1
TS (kg/d) 1,978 5,810 7,788 1
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Cataraqui Bay Ravensview Total
VS in Cake (kg/d) 1,469 2,792 3,887 1
Nitrogen in Cake (kg/d) 59 174 233
Phosphorus in Cake (kg/d) 22 63 85
Centrate
Centrate (m3/d) 62 2 147 3 209
Nitrogen in Centrate (kg/d) 44 2 3 3 47
Phosphorus in Centrate (kg/d)
34 2 29 3 63
Biogas
Biogas (m3/d) 1,061 2,770 3,831 1
Methane in Biogas (m3/d) 611 1,596 2,207 1
Notes: 1. The baseline for biosolid production and biogas yield
under Options 2-5.2. The baseline for dewatering centrate produced
under Options 2 and 4.3. The baseline for dewatering centrate
produced under Option 3.
3.1.3 Cost Analysis The Do Nothing scenario sets out the basis
for comparison. All base options derived hereafter are compared to
the Do Nothing scenario using a change in cash flow over a 20-year
period. It is assumed that the cost for Do Nothing will include the
cost of upgrading the current digesters and undertaking gas
cleaning. This will allow for an apples to apples comparison to the
various option presented. The primary changes are then:
Cost of investment, including engineering costs (15% of
capital), permitting costs, the cost of capital and whenit would be
spent, increase/decrease in operating costs, revenues (primarily
carbon based income), avoidancecosts (tipping fees) and other cash
flow impacts.
Increase or decrease in the use of vehicles for transport of
sludge or cake.
Use of one set of digesters in any of the three potential
locations.
Diverting the SSO to one of the WWTP instead of contracting out
(as one scenario).
Gas cleaning general cost ($2,700,000).
The cost analysis is done with proformas and the final
analytical number is Net Present Value (NPV) using a discount rate
of 5%. For all capital work, estimates for installations are
considered conservative , and a +- 15% factor has been included.
These results are shown in the final NPV calculations Best (lowest
cost and highest revenue) and Lowest (highest cost and lowest
revenue).
Similarly, as there is a wide variance of carbon based gas
prices ($15 to $25 per GJ), these variances have also shown
additively in the Best and Lowest results.
Also of note, as many of the options are interlinked, some
scenarios have been broken out (i.e., dewatering) to assess whether
it is a cost-effective standalone option.
Detailed cash flow statements/pro-formas for all following
scenarios are shown in Appendix 1.
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3.2 Option 2 – Optimize Infrastructure at Cataraqui Bay
3.2.1 Description of Alternative Based on the primary assessment
of alternative stabilization technologies, the following options
were developed for the upgrades to the solids treatment train at
Cataraqui Bay WWTP:
Option 2A – Expansion of the existing MAD process with
capability to operate in TPAD.
Option 2B – Expansion of the existing MAD process with the
inclusion of BH ahead of MAD.
Each of the above two options is described further in the
following sections. For the purpose of developing alternative
sludge treatment options, the following assumptions were made:
The blended sludge from the two plants was assumed to consist of
80% primary sludge and 20% WAS basedon raw sludge generation
quantities from the two plants;
A typical three-day HRT for either thermophilic digester or BH
system was assumed in evaluation; and
The process equipment/footprint will be located on the existing
site.
3.2.1.1 Option 2A – Upgrade Existing MAD to TPAD TPAD utilizes
the advantages of the greater thermophilic digestion rate, which is
generally four times faster than mesophilic digestion. The process
can be operated in either of two modes, thermophilic or mesophilic.
The thermophilic phase is designed to operate at 50 - 60°C with a
three to five-day HRT. Through greater hydrolysis and biological
activity in the thermophilic phase, the system tends to enhance VSD
and gas production as compared to single-phase mesophilic
digestion. The mesophilic phase is designed to operate at 35°C with
a ten-day or greater detention time (Metcalf & Eddy). The
mesophilic phase provides additional VSD and conditions the sludge
for further processing. TPAD process will also accomplish high
pathogen kill to produce CP1 NASM biosolids.
The process upgrades for Option 2A would include:
1. Transporting dewatered primary sludge from Ravensview and
blending with sludge generated at CataraquiBay.
2. One thermophilic digester with a capacity of 3-day HRT.
3. Two mesophilic digesters with a capacity of 15-day HRT
each.
4. Operating the existing secondary digester as digested sludge
holding tank.
5. Two dewatering centrifuges to handle digested sludge.
Figure 3-3 presents the process flow schematic of this
option.
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Option 2A Schematic - Temperature Phased Anaerobic Digestion
(TPAD) at Cataraqui Bay
Thermophilic
Digester
Mesophilic
Digester
Mesophilic
Digester
Secondary
Digester
Dewatering
Dewatering
Cake
Storage
Temperature Phased
Anaerobic Digestion
1
2
3
4
Biogas
Centrate
Ravensview
Sludge Dewatering
Cataraqui Bay
Sludge
Figure 3-3 Upgrades to TPAD at Cataraqui Bay WWTP
3.2.1.2 Option 2B – Inclusion of BH with MAD Biological
hydrolysis (BH) has been shortlisted as a sludge pre-treatment
technology in the preliminary assessment. A BH system provides
similar process benefits as thermophilic digesters by breaking down
complex compounds into simpler forms to enhance digestion
efficiency. BH systems generally increase biogas yield from
domestic sewage sludge by 25% or more and increase the capacity of
existing digester infrastructure by two to three times. These
systems consist of six serial reactor vessels in a plug-flow
process (referred to as “Six-Pack” BH systems) whereby sludge is
heated to 42°C in the first reactor. Over the course of progression
through the remaining reactors, the temperature is reduced to
between 35 - 40°C prior to entering into the mesophilic digesters.
The overall HRT within the BH system is approximately three
days.
To incorporate a BH system upfront of the existing MAD at
Cataraqui Bay, Option 2B would require the following upgrades:
1. Transporting dewatered sludge from Ravensview and blending
with sludge generated at Cataraqui Bay.
2. One “Six-Pack” BH system upfront of mesophilic digesters.
3. Two mesophilic digesters with a capacity of 15-day HRT
each.
4. Operating existing secondary digester as digested sludge
holding tank.
5. Two dewatering centrifuges to handle digested sludge.
Figure 3-4 exhibits a process flow schematic of Option 2B.
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Option 2B Schematic - Biological Hydrolysis + Anaerobic
Digestion (BH-AD) at Cataraqui Bay
Mesophilic
Digester
Mesophilic
Digester
Secondary
Digester
Dewatering
Dewatering
Cake
Storage
Biological Hydrolysis
3
Biogas
4
Centrate
2
1
Ravensview
Sludge Dewatering
Cataraqui Bay
Sludge
Figure 3-4 Upgrades with Addition of BHP at Cataraqui Bay
WWTP
3.2.2 Impact on Existing Facilities
3.2.2.1 Biosolid and Biogas Production Table 3-2 lists biosolid
production and biogas yield under Option 2A and Option 2B side by
side. Both processes could enhance downstream digester efficiency
and biogas yield. With the multi-phase digestion process, the first
step of anaerobic digestion is recognized to be the rate-limiting
step. Through enhanced hydrolysis and biological activity in either
thermophilic or BH step, the overall digestion tends to have
greater VSD and gas production.
Option 2B (BH-AD) is expected to produce less biosolids (24
m3/d) and more biogas (4,408 m3/d) than Option 2A (TPAD). Unlike
TPAD, which operates as a complete-mixed reactor, the BH system
operates in a batch hold process, where only a portion of sludge in
each reactor is transferred forward once per hour. This plug-flow
fashion within the BH system ensures that all sludge spends the
majority of the design HRT within the BH vessels, thereby being
fully hydrolyzed and acidified prior to digestion. Thus, BH-AD
tends to provide a higher VSD than TPAD. Commercial pilot results
and literature data suggest that typical VSD for TPAD is 50% while
BH-AD could achieve 54% VSD.
From a mass balance point of view, biogas yield is proportional
to the amount of VS destroyed biochemically. The gas production
rate of a typical anaerobic digester treating a combination of
primary sludge and WAS should be approximately 0.8 to 1 m3/kg of VS
destroyed. Specific gas production from the two plants was
determined based on the historical plant performance data of VSD,
since the amount of gas produced is a function of temperature, HRT,
and VS loading. The specific gas production rate of 1.65 m3/kg of
VS and 1.47 m3/kg of VS were used for primary sludge and WAS,
respectively, to feature the sewage sludge produced in the two
plants. The two main constituents of biogas are methane (CH4) and
carbon dioxide (CO2). Literature suggests that typical CH4
concentration should be 60% to 70% by volume (MOP 8). Hence, 65% of
CH4 in biogas was used for estimating the biogas yield under
different options.
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Table 3-2 Estimated Biosolid and Biogas Production for Options
2A and 2B Feedstock Option 2A TPAD Option 2B- BH-AD
Volume (m3/d) 116 116
TS Loading (kg/d) 10,051 10,051
VS Loading (kg/d) 7,285 7,285
Biosolids Option 2A TPAD Option 2B Volume (m3/d) 26 24
% Decreased Based on Option 11 96% 92%
TS (kg/d) 6,408 6,117
VS in Cake (kg/d) 3,642 3,351
Nitrogen in Cake (kg/d) 192 184
Phosphorus in Cake (kg/d) 70 67
Centrate Option 2A TPAD Option 2B Additional Centrate (m3/d)2 28
29
Additional Nitrogen Loading (kg/d) 113 121
Additional Phosphorus Loading (kg/d) 86 89
Biogas Option 2A TPAD Option 2B Biogas (m3/d) 3,563 3,857
Methane in Biogas (m3/d) 2,052 2,507
% Increased Based on Option 11 106% 115%
Notes: 1 The percentages of decreased biosolid production and
increased biogas generation are based on the biosolid/biogas
production
Kingston Biosolids and Biogas Detailed Report.docx
under Option 1 – Do Nothing. 2 This is based on centrate
generated in Catarqui Bay under current operating strategy
3.2.2.2 Operational Impact With TPAD and BH-AD, the filamentous
foaming issue is expected to be improved. The thermophilic step in
theTPAD process requires attention to corrosion protection given
the high temperature of operation and handling ofhigh ammonia
levels in the return flow. BH systems operate under milder
conditions (i.e., temperature andpressure).
It should be noted that there would be an additional 28 to 29
m3/d of dewatering centrate from bringing primarysludge from
Ravensview to Cataraqui Bay. This additional centrate containing
high ammonia and phosphoruscontent may affect the treatment
capacity of the existing plant liquid train. Although not being
covered in this report, estimated nitrogen and phosphorus mass
loadings are presented in Table 3-2. In the event that the
additionalorganic loadings cannot be managed in the existing liquid
treatment train, side-stream processing may be required to provide
equalization for the dewatering centrate. This “add-on” side-stream
process will need further evaluation based on the specific
technology selected and design target VS destruction at the
conceptual design stage.
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3.2.2.3 Transportation and Footprint Requirements Sludge
generated from Ravensview will be dewatered and then trucked to
Cataraqui Bay. Implementing either TPAD or BH-AD would require the
sam